Differences in memory dynamics between two closely related parasitoid wasp species

The two closely related parasitoids Cotesia glomerata and C. rubecula (Hymenoptera: Braconidae) coexist in The Netherlands where they occupy slightly different niches. When searching for their caterpillar hosts, they use host plant odours that are released upon feeding by the caterpillars. The species differ in their preference for plant odours during host searching after an associative learning experience. Cotesia glomerata changes its preference for the odour of a particular plant species after an oviposition experience on that plant, whereas C. rubecula does not alter its naïve preference. Using no-choice wind tunnel bioassays we tested, for both species, to what extent oviposition induces memory formation and whether this results from associative learning. In experiment 1 we characterized the temporal dynamics of the memory trace. In both species, oviposition experience induced increased response levels compared to those of naïve wasps. Memory dynamics differed between the species. A single associative learning experience induced a stable long-lasting memory trace that persisted for at least 5 days in C. glomerata. In C. rubecula a memory trace for the odour was present during the first day after the oviposition experience but waned over the following days. From a second experiment we concluded that the increased response could be attributed to a combination of nonassociative and associative learning. We furthermore formulate the learning paradigm for the parasitoids and hypothesize that adaptation to different spatial distributions of the preferred host species has led to the observed differences in memory dynamics.